1. Field of the Invention
The invention is directed to an improved fuel injection valve for internal combustion engines.
2. Description of the Prior Art
Fuel injection valves are known from the prior art in various versions. For instance, in German Patent Disclosure DE 196 50 865 A1, a fuel injection valve is described that communicates constantly with a common rail in which fuel at high pressure is furnished. The fuel injection valve has a housing in which a valve member is disposed longitudinally displaceably in a bore; by its longitudinal motion, the valve member controls the opening of at least one injection opening, through which fuel from a pressure chamber surrounding the valve member is injected into the combustion chamber of the engine. The pressure chamber here communicates constantly with the common rail, via an inlet conduit extending in the housing of the fuel injection valve, and the fuel in the pressure chamber acts in the opening direction on a pressure face embodied on the valve member. A control chamber is also embodied in the housing; it can be filled with fuel and indirectly exerts a hydraulic force, acting in the closing direction, on the valve member. The valve member thus remains in its closed state, given a suitable pressure in the control chamber. If by means of a control valve the pressure in the control chamber is lowered because the control chamber is made to communicate with a leak fuel chamber, then the closing force on the valve member decreases, and the valve member is moved in the opening direction by the hydraulic pressure in the pressure chamber and uncovers the at least one injection opening. If the injection is to be terminated, the control valve is actuated, and fuel flows out of the inlet conduit into the control chamber, so that a high fuel pressure builds up there once again. As a result, the valve member is moved in the closing direction and discontinues the fuel injection through the injection openings.
Because of these very fast closing events, which elapse within only a few milliseconds, pressure fluctuations in the high-pressure region of the fuel injection valve occur both upon the motion of the valve member and upon switching of the control valve; on the one hand, they cause severe mechanical stresses on the housing, and on the other, they have the effect that the subsequent injection begins at a state that is not precisely defined, making accurate metering and an exact determination of the instant of injection impossible. Especially in the region where the control chamber and the inlet conduit communicate, such pressure fluctuations are problematic, because they make precise pressure control in the control chamber and hence precise control of the valve member difficult. This plays a particularly major role in injection events that are broken down into a preinjection, main injection, and/or postinjection, since modern injection systems react quite sensitively to fluctuations in the injection quantity.
The fuel injection valve of the invention has the advantage over the prior art that precisely defined injection events in rapid succession are made possible. Pressure fluctuations that occur in the region of the inlet conduit are rapidly damped, so that very quickly after the control valve has been actuated, a static pressure level is again reached both in the inlet conduit and in the control chamber. Pressure fluctuations in the inlet conduit, which can propagate over the entire fuel column within the inlet conduit, from the pressure chamber back into the high-pressure fuel source, fade quickly because of the damping chamber of the invention.
The inlet conduit communicates with a damping chamber, which is embodied as a hollow space in the housing of the fuel injection valve. Between the inlet conduit and the damping chamber there is a throttle, so that the fuel flowing out of the inlet conduit into the damping chamber, or in the opposite direction, must overcome the resistance of the throttle, and consequently the flowing motion is damped. If pressure changes occur in the inlet conduit, of the kind caused for instance by the opening or closing of the control valve or the valve member, then a higher or lower fuel pressure than in the damping chamber prevails in the inlet conduit. Because of this pressure gradient, fuel will flow through the throttle either from the inlet conduit into the damping chamber or from the damping chamber into the inlet conduit and thus bring about a pressure equalization between the damping chamber and the inlet conduit. Since the fuel flowing back and forth then must pass through the throttle, these flowing motions are damped by friction losses at the throttle, so that very quickly, these pressure fluctuations fade and a static pressure level in the inlet conduit is reached.
In an advantageous feature of the subject of the invention, the damping chamber is embodied as a blind bore in the housing of the fuel injection valve. The throttle is embodied near the inlet conduit, in the communication between the inlet conduit and the damping chamber, in order to achieve an optimal damping effect. Because the damping chamber is embodied as a blind bore, the damping chamber in the housing is simple and economical to produce.
In another advantageous feature, more than one throttle is disposed in the housing, forming a communication from the damping chamber to the inlet conduit. As a result, the damping action of the throttles can be boosted, and by way of various throttles, better adaptation to the requirements of the fuel injection valve can be made.